SPANGDAHLEM, Germany (CNN) -- A U.S. Air Force base in Germany received a bomb threat hours before the sixth anniversary of the 9/11 attacks, military officials said.

U.S. soldiers block the street in front of the main entrance of Spangdahlem Air Base in Germany on Tuesday.

Military police have stepped up security and are taking a closer look at cars and trucks entering the Spangdahlem Air Base following a telephone call threatening to blow the facility up.

Someone speaking German -- with a non-German accent -- called the base Monday evening and issued the bomb warning, according to Iris Reiff, a spokeswoman with the public affairs office at the base.

As well as coming a day before the 9/11 anniversary the incident also occurred a week after the unraveling of a terror plot aimed at U.S. military installations in Germany. Watch how Germany responds to threat »

"We've sort of diverted traffic around the main gate area so each of the security forces can get a complete look at the vehicles from the front and side," said Capt. Kevin Coffman, a base spokesman.

Otherwise, he said, it's "business as usual" on the base, which is in western Germany. German police were working to trace the phone call, but so far no arrests have been made.

Three men, two Germans and a Turk, were arrested last week by German police for allegedly being part of a Islamic Jihad cell that targeted American military installations and other Western targets in Germany.

Investigators said they had begun mixing a massive amount of explosive materials that could have resulted in a strong blast -- stronger than those seen in terror attacks in Madrid in 2004 and London in 2005. E-mail to a friend